The objectives of this study are to determine the precise three- dimensional arrangement of tubulin subunits within the wall of various microtubules, to relate this arrangement to specific bonding sites on the tubule, to explore possible relationship between subunit array transitions an physiological function, and finally, to study the assembly of specific ciliary microtubule both in vitro and in vivo. The specific aims of the project are: 1. To reconcile surface lattices derived from electron microscopic observations of negatively-stained microtubules with those derived from x-ray diffraction of hydrated gels. 2. To determine specific protein dimer subunit locations within the tubule surface lattice for ciliary and flagellar A- and B-subfibers and central pair. 3. To determine whether accessory structures (i.e. dynein arms or radial and circumferentail linkage) bond to lattice- specified locations on the microtubule. 4. To determine whether physiologically-significant surface lattice transitions can occur within microtubules during the motile process. 5. To determine whether chemically-different tubulin dimers can copolymerize and, if so, in what steric manner. 6. To observe the precise temporal and temporal and spatial manner in which microtubule dimers assemble into cilia in vivo.